1. Field of the Invention
This invention relates to the art of saw sharpening machines for the sharpening of saw teeth having alternate high profile pre-cutting teeth and low profile post-cutting teeth and particularly deals with machines for sharpening circular saws having a motor driven grinding disk with first mechanism effecting relative reciprocation between the saw and disk and second mechanism cyclically increasing and decreasing the reciprocating stroke to grind the cutting edge of a pre-cutting tooth and the back face of the adjacent post-cutting tooth and then sharpening the cutting edge of the post-cutting tooth and the back face of the next adjoining pre-cutting tooth with the back face cutting depths controlled to maintain the alternating high and low profiles of adjoining teeth.
2. Prior Art
Circular saw blades particularly useful for the sawing of metals commonly have alternating pre-cutting and post-cutting teeth differentiated in that the tips of the pre-cutting teeth have a higher profile than those of the post-cutting teeth and are appreciably beveled while the post-cutting teeth are either not beveled or only slightly beveled. During the sawing of a workpiece with such circular saws, the pre-cutting teeth operate to form a deep cut while the post-cutting teeth widen the width of the cut.
For sharpening saw blades with pre-cutting and post-cutting teeth, it is necessary to adapt the relative lifting movement after a feed of a saw blade by one tooth division between the sharpening tool and the saw blade to the different heights of the tooth tips of the pre-cutting teeth and the post-cutting teeth. It is usual for this purpose to superimpose on the lifting movement an additional movement so that upon sharpening of a pre-cutting tooth, both the lower as well as the upper dead center of the lifting movement is higher than upon sharpening of a post-cutting tooth. This produces an excessive cutting away of metal from the saw blade because each second tooth is cut uniformly over its entire length from its base to its tip and if, for example, the pre-cutting teeth are regarded as the normal teeth, then the post-cutting teeth are undercut by the amount of the lifting displacement. The loss of metal from the saw is particularly great if the machine is mistakenly adjusted so that the pre-cutting teeth are ground as post-cutting teeth and vice versa.
Finally, such prior known saw sharpening machines produce appreciable mass inertia forces which damage the machine and prevent a smooth operation.